Anxious relatives are searching for missing family members in an Indian city that is home to one of the world's largest religious gatherings, unsure if their loved ones were caught in a stampede that killed 36 people or had simply gotten lost among the tens of millions of pilgrims.

People thronged to the main hospital in Allahabad to see if their relatives were among 36 dead and 30 people injured in the stampede on Sunday evening (local time) at the city's train station. Tens of thousands of people were in the station waiting to board a train when railway officials announced a last-minute change in the platform, triggering the chaos.

An estimated 30 million Hindus took a dip Sunday at the Sangam — the confluence of the Ganges, the Yamuna and the Saraswati rivers — as part of the 55-day Kumbh Mela, or Pitcher Festival. Sunday was one of the holiest days to bathe.

People missing at the Kumbh Mela is the stuff of legend in India and at least a dozen films have been made on the theme. On Sunday, like most other days, volunteers and officials used loudspeakers to give details of children and elderly who were "found" on the river banks, having lost their families in the crowd.

It was unclear how many people were actually missing because of the stampede.

Witnesses blamed police action for the stampede.

"We heard an announcement that our train is coming on platform number four and when we started moving toward that platform through a footbridge, we were stopped. Then suddenly the police charged us with batons and the stampede started," passenger Shushanto Kumar Sen said.

"People started tumbling over one another and within no time I saw people, particularly women and children, being trampled over by others," Sen said.

Police denied they had used batons to control the crowd.

"It was simply a case of overcrowding. People were in a hurry to go back and there were not enough arrangements by the railway authorities," said Arun Kumar, a senior police officer.

Medical superintendent Dr P Padmakar of the main state-run hospital said 23 of the 36 people killed were women.

India's railway minister Pawan Kumar Bansal said an inquiry has been ordered into what led to the stampede.

Indian television stations showed large crowds pushing and jostling at the train station as policemen struggled to restore order.

"There was complete chaos. There was no doctor or ambulance for at least two hours after the accident," an eyewitness told NDTV news channel.

The auspicious bathing days of the Kumbh Mela are decided by the alignment of stars, and the most dramatic feature of the festival is the Naga sadhus — ascetics with ash rubbed all over their bodies, wearing only marigold garlands — leaping joyfully into the holy waters.

According to Hindu mythology, the Kumbh Mela celebrates the victory of gods over demons in a furious battle over nectar that would give them immortality. As one of the gods fled with a pitcher of the nectar across the skies, it spilled on four Indian towns: Allahabad, Nasik, Ujjain and Haridwar.

The Kumbh Mela is held four times every 12 years in those towns. Hindus believe that sins accumulated in past and current lives require them to continue the cycle of death and rebirth until they are cleansed. If they bathe at the Ganges on the most auspicious day of the festival, believers say they can rid themselves of their sins.